500 Error ...can someone please explain this

Good Day...

my issue is...i am ble to access the main website domain
but the domain
/dating
/forum

go to a 500 error...evidently not permissions could not find any of those not right and here is what I get for both extension issues

[Sun Nov 11 01:01:40.993967 2018] [:error] [pid 6872:tid 140648728311552] [client xxxxxxxx:10870] PHP Fatal error:  Allowed memory size of 262144 bytes exhausted (tried to allocate 49152 bytes) in /home/chatsite/public_html/forum/index.php on line 129

[Sun Nov 11 00:32:24.483789 2018] [:error] [pid 7724:tid 140648478869248] [client xxxxxx:10380] PHP Fatal error:  Allowed memory size of 262144 bytes exhausted (tried to allocate 12288 bytes) in /home/chatsite/public_html/dating/inc/header.inc.php on line 23

any help to explain the meaning of those 2 errors and what I need to do to fix it would be greatly appreciated 

thanks

problem solved.....seems I am not the first to make this mistake.....if you change your memory in php.ini and stupidly put MB or mb instead of just M or the whole drawn out number...it will not read it and revert to the default which is evidently the number it was using.... Duh